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 Post subject: CSA Z462 2015 version
PostPosted: Fri Aug 14, 2015 8:34 am 
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Joined: Mon Apr 14, 2008 7:10 am
Posts: 142
There is a statement in the new version of Z462-15 under items 4.3.5.4.1 General: The results of an incident energy analysis to specify an arc flash PPE Category in Table 5 shall be prohibited.

Anyone can provide more inputs here?

Thanks!


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 Post subject: Re: CSA Z462 2015 version
PostPosted: Sat Aug 15, 2015 4:38 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
You can't mix the table method with engineering calculations (incident energy method). This includes labels. This has been a prohibition for a while but not spelled out in the Code.

Under the previous edition, the "PPE categories" were "H/RC values". It was an artificial number or category based on a combination of both hazard and likelihood of injury. Thus for instance depending on the task either level 2 or level 4 PPE could be required for the same equipment. Many practitioners were reading the PPE table "backwards" and putting an H/RC category onto equipment when in fact the incident energy (usually IEEE 1584) method was used. This is wrong. There is a separate Annex for PPE to be used when the incident energy method is used. The label should contain either a PPE category OR incident energy but not both.

That being said, there is also the consequence of multiple edits not coordinating with each other. Along with those changes, the original "task tables" were eliminated and replaced with two separate tables where first the likelihood of injury determined whether or not PPE was required (correctl approach) and second what the PPE level should be based on the equipment. The PPE is the same for all tasks for a given piece of equipment when PPE is required using the table approach. At this point the new "PPE Category" table is substantially the same as the one in Annex H except that it has discrete categories instead of a range of incident energy values. So from a practical point of view the tables can be considered interchangeable but from a purely academic point of view, they are distinct and can't be intermixed.

Note that also using incident energy method, you must now do a risk assessment. So you need to look at likelihood of injury as well, not just calculations based on IEEE 1584.


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 Post subject: Re: CSA Z462 2015 version
PostPosted: Mon Sep 28, 2015 1:30 pm 

Joined: Thu Jul 18, 2013 7:04 am
Posts: 3
CSA Z462-12 : 4.3.3.1 : An arc flash analysis shall not be required when the
(a) Circuit is rated 240V or less
(b) Circuit is supplied by one transformer and
(c) Transformer supplying the circuit is rated less than 125kVA

I could not find this arc flash hazard analysis exception on CSA Z462 - 15. However this is on the IEEE-1584 2002 standard. This case using IEEE calculation method on less than 125kVA, 240V transformer supply system may produce conservative incident energy levels.

What is the best practice for less than 125kVA, 240V transformer supply system for arc flash calculations ?


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 Post subject: Re: CSA Z462 2015 version
PostPosted: Mon Sep 28, 2015 5:38 pm 
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The IEEE 1584 empirical method is only claimed to be valid down to 208 V. However it is based on a single test under 300 V. All other tests failed (self-extinguished). The joint IEEE/NFPA study has found that the cutoff is not tight enough but nothing published yet. IEEE C2 uses 4 cal/cm^2 across the board for 250 V or below. The basic issue is arcs are unstable and frequently weak or self-extinguish but there is not yet an equation for these conditions. So the proper way is to use representative test data or failing that, table results from consensus safety standards such as the 1584 value mentioned or the values from IEEE C2, Table 410-1. Stop trying to model with 1584 or Lee because the assumption (stable arcing) is invalid. And even though the exception in IEEE 1584 is known to have issues (and there are lots more with the empirical formula), its the best available information at this time.


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